Although demand for fossil fuels such as oil, etc. is steadily increasing, oil prices are gradually rising globally with the depletion of oil. In particular, as developing countries such as China, India and the like have achieved gradual economic growth, demand for energy and crude oil is increasing day by day. From the viewpoint of supply, however, crude oil or light oil having low impurity content, especially light crude oil (API of 30 or more), which has been mainly used in oil-refining plants, is produced in gradually decreasing amounts, and crude oil is also becoming heavy.
Hence, crude oil that is inexpensive but contains large amounts of impurities such as organic acids, metal powder, etc. is receiving great attention. Specifically, in regard to oil wells for light oil, heavy oil, crude oil extracted from shallow or deep seas, tight oil, and other unconventional oils, having high impurity content, which have not been developed to date owing to low economic benefits thereof, many countries and companies have become interested in and are actually participating in the development thereof.
In particular, among oil wells for new exploration and oil production, in oil wells of South America including Brazil, Venezuela and Colombia, Africa and some parts of the North Sea, crude oil having high organic acid content is found and produced in a large amount and is being traded at a discount rate of about 7 to 25% depending on the impurity content.
The acidity of crude oil is increased with an increase in the amount of organic acid contained in crude oil. In order to measure the acidity of crude oil, the total acid number (TAN) is used, which means the amount (mg) of potassium hydroxide (KOH) consumed to neutralize the acid contained in 1 g of oil. Crude oil is classified into low-acidity crude oil when the TAN is less than 0.5, acidic crude oil when the TAN ranges from 0.5 to 1.0, and high-acidity crude oil when the TAN exceeds 1.0, and crude oil having high acidity and thus a low price is classified as either acidic crude oil or high-acidity crude oil.
The main ingredient of organic acid, which increases the acidity of crude oil, is widely known to be naphthenic acid. Naphthenic acid is a generic term for saturated carboxylic acids having a naphthene nucleus, which is a paraffinic hydrocarbon having a long chain structure containing cyclopentane, with a carboxylic acid group (—COOH) as a main functional group at the terminal thereof.
In the case where naphthenic acid is fed continuously or in a large amount to a crude oil production or oil-refining process, the surface of the metal in contact with crude oil in plant facilities may corrode, which may cause frequent component replacement, and furthermore, problems, such as plugging of pipes due to the metal compound formed by the bonding of the naphthenic acid and the metal material and inhibition of heat exchange in the facilities, may occur.
However, it is very difficult to effectively remove or treat naphthenic acid because of the variety of detailed chemical structures and compositions thereof.
Techniques for lowering the acidity of crude oil were studied by the world's major oil companies from the 1980s to the early 1990s. After the 1990s, however, such studies were discontinued due to low oil prices, and as a result, there are no processes currently available for lowering the acidity of crude oil.
Crude oil used mainly in oil-refining plants is low-acidity crude oil having TAN of 0.5 or less, but the use of high-acidity crude oil is gradually increasing because of the economic benefits thereof. Currently, high-acidity crude oil is treated in a manner in which the high-acidity crude oil is partially diluted with a large amount of low-acidity light crude oil to thus adjust the TAN to 0.5 or less, and is then introduced to an oil-refining process together with a corrosion inhibitor. Briefly, there is required a technique for efficiently lowering the acidity of crude oil by removing organic acids from crude oil.
Meanwhile, crude oil is usually transported to oil-refining facilities via pipelines, oil tank trucks or oil tank ships. Here, when the transport conditions are low temperature and high pressure, a gas hydrate may be formed.
A gas hydrate is a solid material, and is configured such that small gas molecules such as methane, ethane, propane, carbon dioxide, and the like are physically bonded to the voids in the three-dimensional lattice structures formed by the hydrogen bond between water molecules, rather than being chemically bonded. Since such a gas hydrate may block pipes or damage storage tanks, it must be prevented from being formed using an inhibitor.
The gas hydrate inhibitor may cause economic and environmental problems due to the disposal thereof, including separation and then discharge to the sea, after transport of crude oil.
The present inventors have ascertained that when a gas hydrate inhibitor, such as mono-ethylene glycol (MEG), di-ethylene glycol (DEG), tri-ethylene glycol (TEG), methanol or derivatives thereof, is reacted with crude oil in the presence of a catalyst, organic acids may be removed from the crude oil and thus the acidity of the crude oil may be lowered.
Furthermore, the present inventors have paid attention to the problem in which the use of an alkaline earth metal-based catalyst including magnesium (Mg) may cause catalyst deactivation because magnesium may dissolve in water, which is a byproduct of the organic acid removal reaction, or may participate in the reaction, and thus have been ascertained that the above problem may be solved using tungstophosphoric acid (TPA) as a catalyst, rather than the alkaline earth metal-based catalyst including magnesium, thus culminating in the present invention.